concat type/provider broken since 3.7.1

I set up a GIT repository at https://github.com/aroth-arsoft/puppet-type-concat with my concat type+provider.

When i'm running the run_concat_test script using puppet version 3.7.0 (or before) the script creates two files:
/tmp/concat_test2 which contains
concat1
concat2
concat3

and /tmp/concat_test_redir
concat1
concat2
concat2_1
concat2_1_1
concat2_1_2
concat2_1_3
uptime=1:01 hours
concat2_3a
concat2_3b
concat3

If i run the same script with puppet 3.7.1 the /tmp/concat_test_redir file is empty and the /tmp/concat_test2 is correct.